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Tsubouchi, Masaaki; Kumada, Takayuki
no journal, ,
We have introduced a novel etalon device for THz laser pulses to generate THz laser pulse trains. The etalon usually consists of a pair of the high reflective mirrors. Therefore, a large amount of input light is reflected by the input mirror, and cannot be transferred to the pulse train efficiently. We have solved this intrinsic problem of the etalon by using an optical switch. Our THz etalon consists of a thin silicon (Si) plate as an input coupler and a glass coated by the indium tin oxide (ITO) as an output coupler. The Si plate is transparent for THz light, and the ITO membrane strongly reflects it. After the THz pulse transmits the Si plate, the Si is irradiated by a UV light pulse to generate the plasma sheet which strongly reflects the THz light. The UV light operates as an optical switch which traps the THz pulse in the etalon cavity. The small portions of THz light are transmitted through ITO in each round trip, and form the pulse train. In this study, we have demonstrated the THz etalon, and efficiently obtained the THz pulse trains which have comb-shaped spectra.
Otobe, Tomohito; Shinohara, Yasushi*; Sato, Shunsuke*; Yabana, Kazuhiro*
no journal, ,
We calculate the modulation of the optical properties of a diamond under an intense static fields and intense mid-infrared (MIR) light fields employing the time-dependent density functional theory (TDDFT). We solve the time-dependent Khon-Sham equation with real-time and -space method under time-dependent vector fields. Our results well reproduce the exponentially tail of absorption below the band gap and the Franz-Keldysh oscillation above the band gap.
Kondo, Masato; Oshima, Yasuhiro*; Tsubouchi, Masaaki
no journal, ,
We investigated the dielectric relaxation of aqueous ionic solutions by applying the terahertz time-domain spectroscopy (THz-TDS) to obtain the global picture of ionic hydration. We measured the dielectric spectra in the 0.2-1.8 THz region, and found the significant effects of dissolved cations on the imaginary part of the spectra. Especially in the high frequency region, the dielectric spectra increased in intensity as compared to that of pure water, which cannot be explained by the hydration effect within first hydration shells. This result indicates the dielectric relaxation was enhanced in the ionic solution, implying the dissolved ions weaken the hydrogen bonding of water beyond ion hydration shells.